The critical problem in this study was that despite the crucial role mathematics education plays in promoting scientific and technological development, girls’ performance in the subject as compared to boys (especially in mixed schools) had been quite dismal. It is for this reason that the purpose of the study was to investigate the school related factors influencing girl’s performance in mathematics in mixed secondary schools in Kobujoi Division, Nandi South District. To achieve the objectives of the study, the study examined factors such as attitudes held by teachers and students in Mathematics, teaching - learning resources, KCPE performance, role models, and teachers’ qualifications. The study targeted all the ten mixed secondary schools in the Division; ten head teachers, twenty mathematics teachers, all girls in forms three and four totaling 360. Stratified sampling technique was used to pick four mixed secondary schools basing on their boarding status (boarding, day & boarding, day). Within the sampled schools, purposive sampling technique was used to pick head teachers, forms three and four mathematics teachers and students (girls). Simple random sampling technique (balloting) was used to pick girls from forms three and four making 10 per class. Thus, the sample selection was made up of 80 students, 8 teachers, and 4 head teachers, all totaling 92 respondents
